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Let's suppose I encrypt a plaintext with one key and a nonce in CTR block cipher mode of operation.

Can I reuse the nonce with another key in another plaintext if I start the block counting with different counters than those used in the first plaintext? I mean (for example), encrypt the first plaintext stopping at the counter 999 and start in the next plaintext with the same key and nonce with counter 1000 and onwards.

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    $\begingroup$ Consider that two 1000-block plaintexts encrypted with counter values 0..999 and 1000..1999 is not much different from having one longer 2000-block plaintext that gets encrypted with counter values 0..1999. $\endgroup$
    – ilkkachu
    Mar 20 at 21:03

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Yes, you can.

While using CTR (GCM, ...) mode of operation, you absolutelly CAN NOT reuse combination of KEY and IV (and counter value for ANY block).

As long as you keep records of what combinations of KEY and IV (and for what counter values), and make sure you do NOT reuse same KEY+IV+counter; your scenario if fine.

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